This invention pertains to a method and apparatus for the rapid pyrolysis of lignocellulosic products, especially forest waste.
In the wood transformation industry, wastes comprised of bark, shavings, sawdust and stumps constitute up to 16% in weight of the usable wood. In view of the increase in energy costs, it has become feasible to recover energy contained in that waste.
The most widespread means of energy recovery is combustion of such waste in boilers. Steam is thus obtained which is either used for heating or for producing electricity. But this solution displays some disadvantages. The boiler must be adapted to the efficient combustion of the waste, the hearths are sizeable and the boilers are large. The thermal power generated by these boilers is extremely difficult to modulate or control, which leads to a lack of flexibility which does not make it possible to adapt this power to instant consumer needs that fluctuate most of the time. Finally, the smoke must be treated prior to its ejection into the atmosphere, which leads to the installing of often costly purification devices.
Another more recently evolved means of energy recovery is the gasification of waste. Gas produced by this method net caloric values of about only 1,000 to 3,000 Kcal/Stdm.sup.3, however, as a result of dilution by carbon dioxide and/or nitrogen, and this gas is thus better suited to organic synthesis uses due to its hydrogen and carbon monoxide contents. Furthermore, the gas generators which are currently used for gasification are complicated by the fact that the transformation of solid fuel into gas under the action of air or oxygen and ultimately of water vapor most often takes place at the same time as pyrolysis whereas, in order to produce perfectly purified gas, it should only take place after pyrolysis and the break-up of pyrolysis products. Hence, the incompletely transformed products pollute the gas which is obtained and make it unsuitable for direct use without special treatment.